Single-Acting Landing Gear Actuator With Two-Stage Outlet Damping
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Solution Overview
Problem
Dual acting actuators for aircraft landing gear assemblies are complex, expensive, heavy, and prone to malfunction, and there is a need for a simpler actuator that can manage high loads to reduce impact on the landing gear assembly.
Innovation Solution
A single acting actuator with a housing, piston, and piston rod, featuring first and second pressure chambers with outlets that control fluid flow to slow piston movement, providing a snubbing effect to reduce impact loads, and allowing for a compact and lightweight design by connecting the pressure chambers to reduce fluid requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a dual acting actuator is used to manage high loads and control piston movement in both directions, then the actuator can handle extension and retraction forces, but the device complexity, weight, and cost increase
Solution Approach 1:
The patent extracts the retraction function from the actuator itself, allowing gravity and aerodynamic forces to handle landing gear retraction while the actuator focuses solely on providing extension force. This eliminates the need for a dual-acting mechanism, reducing complexity while maintaining force capability in the critical extension direction
Solution Approach 2:
The landing gear assembly uses its own weight and aerodynamic forces to assist in the retraction process, eliminating the need for an active retraction mechanism. The system serves itself by utilizing environmental forces (gravity and airflow) to perform part of the work that would otherwise require additional actuator complexity
2Force
If a dual acting actuator is used to provide controlled movement in both directions, then the actuator can manage high loads, but the weight of the actuator increases
Solution Approach 1:
The patent removes the retraction mechanism from the actuator design, allowing the landing gear to retract using its own weight and aerodynamic forces. This extraction of the retraction function significantly reduces actuator weight while maintaining the ability to handle high extension loads when needed
Solution Approach 2:
The patent accepts that the landing gear will experience high impact loads during deployment but designs the actuator to be simple and lightweight, relying on the rarity of such high-stress events. The actuator is optimized for the more frequent low-stress operation rather than being over-engineered for rare high-load scenarios
3Speed
If outlets are opened during the first stage of piston movement to allow fluid flow, then the piston can move quickly, but impact loads increase towards the end of travel
Solution Approach 1:
The patent implements periodic control of the outlets, opening them during the first stage of piston movement to enable quick fluid flow and rapid piston travel, then closing them during the second stage to prevent impact loads. This time-based switching of outlet states allows the system to achieve both fast movement and impact reduction
Solution Approach 2:
The outlets are opened in advance during the first stage of movement to allow actuator fluid to flow and prepare the system for rapid piston travel. This preliminary opening of outlets enables the piston to move quickly while the system is still in a controlled state, before the potentially harmful impact phase begins
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The single acting actuator effectively reduces impact loads on the landing gear assembly, allows for a compact and lightweight design, and simplifies the actuation system, addressing the complexity and weight issues of dual acting actuators while maintaining efficient operation.
Implementation Method 1
the piston being movable relative to the housing from one of the retracted and extended positions to the other by a resultant force on the piston due to the pressure of actuator fluid in the first and second pressure chambers
Implementation Method 2
in a first stage of the relative movement the first and second outlets are open thereby allowing actuator fluid to flow out of the pressure chamber through the first and second outlets and in a second stage of the relative movement the second outlet is open but the first outlet is closed, thereby acting to slow the relative movement of the piston with respect to the housing
Data Source
AI summary
A single acting actuator for an aircraft landing gear assembly is disclosed having a piston mounted in a cavity and moveable relative to a housing between a retracted position and an extended position, the piston dividing the cavity into first and second pressure chambers. At least one of the pressure chambers is associated with first and second outlets, with the actuator being arranged such that, in respect of the relative movement in which the pressure chamber is the decreasing volume pressure chamber, in a first stage of the relative movement the first and second outlets are open thereby allowing actuator fluid to flow out of the pressure chamber through the first and second outlets and in a second stage of the relative movement the second outlet is open but the first outlet is closed, thereby acting to slow the relative movement of the piston with respect to the housing.